The invention relates to a scanner that uses both optics and image processing to produce a scanned image, and more particularly to a scanner using an array of lenses that produce inverted sub-images for which the inverted data thereof is transposed and assembled into a complete image.
Prior art scanners, such as might be used in a stand-alone manner or in a photocopier or facsimile machine, typically scan one line of pixels of the object document at a time. Such prior art which utilizes arrays of imaging lenses typically performs 1:1 imaging, i.e., neither reducing or enlarging, using non-inverted optical images. An example of a lens system that produces such 1:1 non-inverted images is an array of gradient-index (GRIN)lenses. An advantage of using the GRIN-lens array is that a 1:1 non-inverted imaged can be produced entirely with optics, i.e., without the need for image processing.
Currently, the highest resolution GRIN lens array-based scanner is 300-400 dots per inch (dpi), but a 600 dpi GRIN lens array-based scanner is anticipated to be commercially available soon. The technology for a 1200 dpi GRIN lens array-based scanner is not yet, and might not be for a long time, available.
A disadvantage of a GRIN lens array-based scanner is that it has a poor depth of field (DOF), i.e., a DOF less than 0.5 mm. A typical DOF for prior art GRIN lens array-based scanner is 0.2 mm or 0.3 mm.
It is desirable to have a DOF that is greater than 0.5 mm, and preferably 1.0 mm or better. A smaller DOF produces a scanner that is not robust. For example, if a piece of paper does not lie completely flat on the platen of the scanner because it has a crease in it, then the typical prior art DOF of 0.2 mm or 0.3 mm causes the image corresponding to the crease in the paper to be out of focus.
Having a depth of focus of 0.3 mm or less means that the mechanical positioning tolerances of the platen, lens array and optical-energy to electrical-energy converter must be less than 0.3 mm. This is difficult to manufacture with a low defect rate.
As resolutions increase, the problems of GRIN lens array-based scanners will increase. For a given GRIN lens array, changing the optical-energy to electrical-energy converter from 600 dpi to 1200 dpi will cut the DOF approximately in half. Thus, if the DOF was 0.3 mm at 600 dpi, it will be approximately 1.5 mm at 1200 dpi with the same GRIN lens array.
Prior art scanners that scan one line of a document at a time typically have an imager (for converting the optical image into electric signals) that is the width of the line to be scanned. For a document on 8.5 inch by 11 inch paper that is in the portrait (rather than the landmark) format, the imager needs to be 8.5 inches wide. Such a prior art imager is formed from a sequence of smaller, e.g., 1 inch, imagers, e.g., charge coupled devices (CCDs), connected end-to-end together.
The joint between two CCDs represents a non-imaging area on the order of one picture imaging element (pixel) wide. When used with a GRIN lens array, the non-imaging joints in the composite imager result in lost image data because the GRIN lens array produces a 1:1 image, a small portion of which impinges on the joints. Thus, either image information at the joints is lost or interpolation must be performed on the image data derived from the image formed by a GRIN lens array, which is a problem.
An objective of the invention is to improve upon the deficiencies of the prior art GRIN lens array-based scanners. In particular, an objective of the invention is to provide a scanner having a more robust depth of field (DOF) than the prior art GRIN lens array-based scanners. Also, an objective of an invention is to provide a scanner that is more economical to produce than the prior art GRIN lens array-based scanners.
These and other objectives of the invention are achieved by providing an imaging apparatus comprising: a lens array including a plurality of lenses, each lens in said lens array forming an inverted optical image of a portion of an object; an imager to convert the plurality of inverted optical images into image data; and a baffle array including a plurality of parallel light absorbing baffles, each baffle in said baffle array forming a light absorbing border between adjacent optical paths, said paths lying between said lens array and said imager.
These and other objects of the invention are also fulfilled by providing a method of calibrating an imaging apparatus (the imaging apparatus including a lens array, each lens in said lens array forming an inverted optical image of a portion of an object, an imager including an optical-energy to electrical-energy converter to convert the plurality of inverted optical images into a plurality of inverted image data sets corresponding thereto, respectively, each of said inverted data sets being a sequence of data having a beginning part, a middle part and an end part, and a controller to filter said sequence so as to discard said beginning and end parts and retain said middle part, and a baffle array, each baffle in said baffle array forming a light absorbing border between adjacent optical paths, said paths lying between said lens array and said imager), the method comprising: providing a calibration pattern of bars alternating between a first color and a contrasting second color, wherein widths of said bars of said calibration pattern are fixed such there is a first transition and a second transition in said calibration pattern from said first color to said second color approximately aligned with a first and second edge, respectively, of each lens in said array thereof; determining, at least indirectly based upon each of said inverted data sets, a first and second indicator of where said first transition and said second transition occur in each of said inverted data sets, respectively; and storing said first and second indicators for each of said inverted data sets.
These and other objects of the invention are also fulfilled by providing a method of forming an imaging apparatus, the method comprising: forming a lens array including a plurality of lenses, each lens in said lens array refracting an inverted optical image of a portion of an object; providing an imager to convert the plurality of inverted optical images into image data; forming a baffle array including a plurality of parallel light absorbing baffles separated by air gaps and one of a top baffle and a bottom baffle; aligning said lens array to a first end of said baffle array such that each baffle in said baffle array forms a light absorbing border between adjacent optical paths, said paths lying between said lens array and said imager; attaching said lens array to said baffle array; and attaching said imager to said baffle array.
The foregoing and other objectives of the present invention will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.